The object of the research described in this proposal is to expand our knowledge of development in general and of meiosis in particular, using as a model system the meiotic life cycle of the yeast Saccharomyces cerevisiae. We intend to use a set of Gamma-Charon 28 yeast chimeric bacteriophage, each of which contains a gene which is transcribed in meiotic cells but either much less or not at all in mitotic cells, to explore the mechanism of regulation of gene expression during development. In order to do this we will distinguish those genes which are required for sporulation (sporulation-essential) from the sporulation-specific ones by using transformation to disrupt the chromosomal copy and then determining the phenotype of the homozygous mutant cells. We already know that the transcripts from several of these genes appear in the cells at about meiosis I. We will determine the time and rate of synthesis and breakdown of the transcripts from these genes, and we will determine when they appear on polysomes, in order to ascertain whether post-transcriptional regulation occurs. We will construct fusions of these genes with the E. coli lac Z gene, determine whether regulation of the fused gene is normal, and then use the fusion products to select for mutations, both cis and trans acting, which affect regulation. All mutants isolated will be subjected to standard genetic analysis. We expect from this work to learn about the molecular basis of the regulation of gene expression during development; in particular, we hope to begin to understand the way in which temporal cycles are controlled. This knowledge will help us to approach rationally problems in birth defects, neoplasia, and immunoonotology, as well as contributing to our understanding of basic biology.